Metallurgical process control of oxygen content

ABSTRACT

A metallurgical process is controlled by directly measuring the oxygen content of a specimen taken from the melted charge. The specimen is subjected to neutron radiation, and the radiation of the resulting 16N isotopes is measured. Addition agents are then used to alter the oxygen content of the charge to a desired value. Preferably, the specimen is bombarded simultaneously with a specimen of known oxygen content, and the differences in radiation of the known and unknown specimens are automatically displayed and/or used to effect the desired additions.

I United States Patent [151 3,66 1,559

Horvath et al. 1 May 9, 1972 [54] METALLURGICAL PROCESS [56 References Cited CONTROL OF OXYGEN CONTENT UNITED STATES PATENTS [72] inventors: Aurel Horvath; Gellert Repasi, both of D j Elek $18119; Bruno Vol-sail, 2,253,574 8/1941 Norbeck ..73/19X both of B p all of g y 2,991,684 7/1961 Wever et al ..73/ 19X [73] Assignees: M.T.A. Koz onti Fizikai Kutato lntzet, g: i f j 5 m D F 3,251,217 5/1966 Evens et al ..73/1 9x t Part 3,378,478 4/1968 Kolodney et al ..204/195 5 0 3,403,090 9/1968 Tajiri et al ..204/l95 3,432,288 3/1969 Ardito et al ..75/60 [22] Filed: Dec. 3, 1968 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. White [2!] Appl' 780855 Attorney-Young and Thompson [57] ABSTRACT [30] Foreign Appncation p i i Dam A metallurgical process is controlled by directly measuring the oxygen content of a specimen taken from the melted charge. Dec. 6, 1967 Hungary ..MAl788 The pecimen is subjected to neutron radiation and the radia. tion of the resulting N isotopes is measured. Addition agents [52] U.S. Cl ..75/45, 73/19, 75/49, are then used to alter the oxygen content of the charge to a 75/58, 75/60, 75/93, 250/71.5 desired value. Preferably, the specimen is bombarded simul- 51 Int. Cl. ..C2lc 7/06, oon 1/20 i a t i Xygen 3 the [58 1 Field of Search ..75/60, 43, 45, 49, 58, 93; dfierences and are automatically displayed and/or used to effect the desired additions.

2 Claims, 3 Drawing Figures 1 f fill/1% l? V I G 4 9W1. 1* I 1 2 3 I) PATENTEDMAY 9 I972 3.661.559

INVENTORS 14 M51. Ham 4 m 6544 :27 50,434

ATTORNEYS METALLURGICAL PROCESS CONTROL OF OXYGEN CONTENT This invention relates to the production of metals and alloys, including iron and its alloys in a reproduceable quality. The procedure is suitable to control metallurgical reactions occurring in a non-reducing furnace atmosphere. The production in reproduceable quality is ensured by the control of various phases of the metallurgical process in the exact knowledge of the oxygen content of the heat. According to the procedure the quantity of oxygen (or equivalent) needed to remove the accompanying substances and contaminants, as well as the quantity of additions (deoxidizing substances) needed to bind or remove residual oxygen in the heat is determined on the basis of the prevailing oxygen content. These quantities are computed stoichiometrically.

The production of various metals and alloys by non-reducing melting techniques is based, in the conventional procedures as known at present, on the change of the oxygen content in the heat. Since however a method for the rapid, accurate and continuous determination of oxygen is at present not available, the charge treatment is based on the changing quantity of other accompanying materials or on analytical methods, which are suitable for the indirect assessment of oxygen present in the heat. Thus, for instance in steel production the oxygen content of the steel bath is concluded from the changing carbon content of the heat or the colour and character of the samples taken from the melted slag.

Not knowing the exact oxygen content of the heat retards the melting process and increases the costs of melting.

The melting process is retarded by the lack of knowledge of the oxygen content, because:

a. if a larger or smaller amount of oxidizing material is used than required to remove the accompanying materials or contaminants in the furnace, this may cause the danger of cooling down or overheating the bath;

b. the amount of slag forming materials and therefore the amount of slag cannot be predetermined;

c. the deoxidation period needed to remove residual oxygen from the heat cannot be forecast with the required accuracy.

The cost of the melting process is increased by the lack of knowledge of the oxygen content, because:

a. the deoxidizing additions with a view to safe oxygen removal are used in excess;

b. the deoxidizing additions used in excess cause the chemical composition of the metal alloys i.e. steels to vary over a wide range;

c. since the oxygen content of the heat cannot be controlled the amount of non-metallic (oxidized) inclusions may increase to an extent where they unduly increase the defective products, due to inherent blemishes of the metal.

To determine the oxygen content of metals and alloys various methods are known. The most widely used among them is vacuum melting or melting under a blanket of protective atmosphere, and the measurement of the CO gas thus generated. However this method, due to the too long test period and unreliable results (the error caused by oxides difficult to reduce) is not suitable to control the metallurgical reactions. Another well known method is spectroscopic analysis the results of which however are so variable that to calculate on the basis of these data would lead to major errors in charge treatment. Recently nuclear methods have become known. The use of some of these methods involves extremely costly equipment (cyclotron, linear accelerator, betatron) thus they are not suitable for industrial use. Others involve the application of relatively small equipment suitable for use in the industry (neutron generator) however no analytical method or equipment is known which would give reliable results under plant conditions in a suitably short time during the charge treatment phase. Thus, hitherto, there was no method suitable to control the melting technique of metals and alloys on the basis of the oxygen content. The methods described above give the results of oxygen-content determinations either subsequently, or serve only to increase to accuracy of analytical results, therefore due to their slowness or relative inaccuracy are not suitable to be used in the control of metallurgical processes, on the basis of the oxygen-contents thus determined.

The essence of the invention is the direct control of the metallurgical processes used to produce metals and their alloys on the basis of the exact and continuous determination of the oxygen content. With knowledge of the oxygen content the amount of oxidizing additions needed in the oxidizing stage of the production of metals and their alloys and the amount of deoxidizing additions needed in the reducing phase is calculated. The calculation is based, in the knowledge of the exact oxygen content on the stoichiometrically required amount.

The steel industry may be taken as an example for the application of the control of metallurgical processes based on the oxygen content. The major characteristic of steel production is to reduce gradually the initial carbon content of the heat to the predetermined final content. To the prevailing carbon content corresponds an adequate oxygen content, which may be determined on the basis of the state of equilibrium known from the literature and increases with decreasing carbon content. In order to be able to determine the amount of oxidative additions needed for decarburization it is essential to know the oxygen content of the furnace charge at the commencement of the decarburization process. The additions of the oxidative additions at a correct rate ensures the optimal rate of decarburization.

Since the oxygen content in equilibrium with the final carbon-content is higher then permitted in steel without the impairment of its mechanical and other properties the superfluous oxygen content has to be removed or to be reduced well below the equilibrium level. The more accurate the knowledge of the oxygen content the more exactly the amount of the oxygen binding or deoxidizing substances needed may be determined. The advantage of adding deoxidizing substances in an amount controlled in accordance with the oxygen content is that they are added in the stoichiometrically determined quantity and thus the amount of the accompanying substances is reduced, thereby reducing the proportion of substandard goods, due to the inherent blemishes of the steel caused by the inclusions. This achievement manifests itself in the proportionate improvement of the output.

According to the procedure of this invention a specimen of defined size and simple geometrical shape is prepared from the metal taken from the heat and the oxygen atoms contained in the specimen are transformed by O/n p/"N nuclear reaction into radiant isotopes and the radiation of N isotope is measured. The establishment of the flux of the neutrons during radiation treatment, or the normation of the change occurring in the specimen to the same flux level, is carried out by the count-partition time variation method.

The schematic diagram of an analyzer according to one embodiment of the invention is shown in FIG. 1.

The neutron source 1 of the equipment is contained in wall 2 serving as means of protection.

The sample transporting tube 3 and neutron flux meter transporting tube 4, both ending in measuring chamber 5, pass in front of the neutron source. Detector 6 is placed in the chamber to measure the radiation of the sample and detector 7 to measure the radiation of the specimen of known oxygen content. The chamber jacketed sample radiation meter 8 is connected to detector 6 and radiation measuring instrument 9 for the reference specimen is connected to detector 7. Printing device 10 for gathered data and automatic operation control device 11 also form a portion of the equipment.

Radiation source 1 converts the oxygen atoms contained in the sample into radioactive isotopes and the radiation of the radioactive isotopes thus formed and the flux of the radiation source are measured and evaluated by instruments 5 to 10.

The sample input is at 12 and it is taken out at 13 as shown in FIG. 1.

The following advantages may be achieved by the invention:

- the quality of metals and their alloys can be reproduced,

a saving is achieved in oxidizing and deoxidizing substances;

the metals and their alloys thus produced are of a more even quality;

the output of the products manufactured from the metals and their alloys thus produced is increased.

The basic principles of the invention are demonstrated by way of example by the technology worked out for steel production.

The amount and quality of deoxidizing agents to be added to the heat for deoxidizing, to a given oxygen-content, is calculated and given out in technical directions as determined on the basis of the oxygen content of specimens taken from the steel bath at predetermined times.

On the basis of the oxygen content in the sample taken during discharge, it is determined whether further deoxidizing is needed and if this is the case, the quantity of the deoxidizing agent to be added during casting. The latter determination is simplified by the use of the nomogram as seen in FIG. 2. In this nomogram the specific amount of Al to be added during casting may be directly read as a function of the carbon and oxygen contents as determined by analysis.

FIG. 3. shows the flow diagram of one of the possible applications of the procedure. 1', 2 and 3 are samples taken at various phases of charge treatment, 4 the metal bath, 5' the instrument for oxygen determination, 6' the display of oxygencontent, 7' the means for determination of the additions, 8' and 9' the addition means for various materials, 10' and 11' the storage means for various additives and 12' the means for treatment of the sample.

The economic results derived from the application of the procedure are manifested by the higher output due to a more even quality and this amounts to about 2-3 percent.

What we claim is:

l. A method for the control of a metallurgical process, comprising establishing a bath of molten metal of unknown oxygen content, withdrawing from the bath a specimen of metal, subjecting said specimen to neutron radiation to produce N isotopes, detecting the radiation of said isotopes, and adding to the bath material to change the oxygen level thereof determined by said detected radiation.

2. A method as claimed in claim 1, and exposing to said neutron radiation a specimen of known oxygen content, detecting the radiation of the N isotopes produced by radiation of said known specimen, determining the difference in detected radiation of said known and unknown specimens, and effecting said addition in response to said determined difference. 

2. A method as claimed in claim 1, and exposing to said neutron radiation a specimen of known oxygen content, detecting the radiation of the 16N isotopes produced by radiation of said known specimen, determining the difference in detected radiation of said known and unknown specimens, and effecting said addition in response to said determined difference. 